﻿using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

public partial class validate_CheckCode : System.Web.UI.Page
{
            protected void Page_Load(object sender, System.EventArgs e)
            {
                this.CreateCheckCodeImage(GenerateCheckCode());
            }

        private string GenerateCheckCode()
        {
            int number;
            char code;
            string checkCode = String.Empty;

            System.Random random = new Random();

            for(int i=0; i<5; i++)
            {
                number = random.Next();

                if(number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('a' + (char)(number % 26));

                checkCode += code.ToString();
            }

            //Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
            Session["CheckCode"]=checkCode;
            return checkCode;
        }

        private void CreateCheckCodeImage(string checkCode)
        {
            if(checkCode == null || checkCode.Trim() == String.Empty)
                return;

            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 17.5)), 35);
            Graphics g = Graphics.FromImage(image);

            try
            {
                //生成随机生成器
                Random random = new Random();

                //清空图片背景色
                g.Clear(Color.White);

                //画图片的背景噪音线
                for(int i=0; i<25; i++)
                {
                    int x1 = random.Next(image.Width);
                    int x2 = random.Next(image.Width);
                    int y1 = random.Next(image.Height);
                    int y2 = random.Next(image.Height);

                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }

                Font font = new System.Drawing.Font("Arial", 20, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                String code2="";
                for (int i = 0; i < checkCode.Length; i++)
                    code2 = code2 + checkCode[i] + "  ";
                g.DrawString(checkCode, font, brush, 2, 0);

                //扭曲
                double dBaseAxisLen = (double)image.Height;
                for (int i = 0; i < image.Width; i++)
                {
                    for (int j = 0; j < image.Height; j++)
                    {
                        double dx = 0;
                        dx = 3.14159 * (double)j / dBaseAxisLen;
                        dx += 1;
                        double dy = Math.Sin(dx);

                        //取得当前点的颜色
                        int nOldX = 0, nOldY = 0;
                        nOldX = i + (int)(dy * 2);
                        nOldY = j;
                        System.Drawing.Color color = image.GetPixel(i, j);
                        if (nOldX >= 0 && nOldX < image.Width && nOldY >= 0 && nOldY < image.Height)
                        {
                            image.SetPixel(nOldX, nOldY, color);
                        }
                    }
                }

                //画图片的前景噪音点
                for(int i=0; i<100; i++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);

                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }

                //画图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }


    }

